Results of a recent study at the MIT-CRC showed a distinct differences in fed state 13C02 production between 2 diets wherein leucine was administered as a free amino acid mix or as part of an intact protein, casein. The experiment cited was for 8 hours and had a leucine content of 115 mg/kg/d. This experiment is aimed at addressing the following: 1) Is the pattern observed in our earlier experiments true for a 24 h period? 2) How would a leucine diet of 40 mg/kg/d (MIT level) effect kinetics under these conditions? 3) Would the route of tracer administration (oral vs I.V.) have any effect under these conditions?